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https://hdl.handle.net/20.500.12451/317

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Enhancing heat transfer performance in elliptical tubes with nano fluids: A numerical case study
(Taylor and Francis Ltd., 2025) Danışmaz, Merdin; Akdağ, Ünal
This study focuses on investigating the thermal performance of elliptical tubes in heat transfer applications with three different working fluids, namely water, CuO-water nano fluid, and Al2O3-water nano fluid. The research emphasizes the role of channel cross-sectional geometry and the utilization of nano fluids in enhancing heat transfer for four different elliptical aspect ratios with the same hydraulic diameter. To ensure fully developed hydrodynamic flow conditions and eliminate pipe outlet effects, a test section for flow analysis was identified at the midsection of the designed pipe geometry. Numerical simulations were conducted using ANSYS 2020 R2 commercial software for low Reynolds numbers, which yield laminar flow, to analyze the impact of the elliptical cross-sectional geometry and heat transfer characteristics on the flow. The effects of nano fluids and the use of elliptical pipes on heat transfer were validated against empirical formulas based on Nusselt numbers. The results indicate that nano fluids exhibit superior heat transfer performance compared to water across all elliptical aspect ratios investigated. Although the best thermal performance belongs to the CuO nanoparticle fluid, it was understood that the use of Al2O3 fluid would also be beneficial due to its accessibility and being more economical. Moreover, it was determined that increasing the ellipticity under the specified flow conditions improved the heat transfer efficiency. Overall, this research provides a comprehensive analysis of the interaction between channel geometry, nano fluid selection, and heat transfer performance, offering valuable insights for designing more effective heat transfer systems in various engineering applications.
Enhancing the Strength of Polylactic Acid Material by Bonding Glass Fiber-Reinforced Polymer Composite Plates With Various Fabric Weights and Orientations
(John Wiley and Sons Inc, 2025) Horasan, Murat; Saraç, İsmail; Benli, Semih
This study investigates the impact of applying bidirectional glass fiber fabric-reinforced polymer (GFRP) composite coatings to the top and bottom surfaces of three-dimensional printed polylactic acid (3D-printed PLA) parts on their mechanical properties. The study uses tensile, three-point bending tests, and finite element method (FEM) analysis to examine how the coatings affect the PLA parts. The objective is to enhance the mechanical properties of PLA parts produced by additive manufacturing (AM) so that they can be used in applications requiring high strength. The study involves bonding bidirectional GFRP composites to the outer surfaces of 3D-printed PLA parts using epoxy adhesive to create sandwich-structured composite materials. Two different types of bidirectional glass fiber fabric (GFF) with low weight (25 g/m2) and high weight (100 g/m2) are used as reinforcement materials, while epoxy serves as the matrix material in the composite coatings. The production process involves creating bidirectional-GFF reinforcement materials in two layers, cut at 0° and 45° orientation angles, and bonding them to PLA specimens with epoxy adhesive. Mechanical tests demonstrate increased tensile and flexural strength of PLA parts coated with bidirectional GFRP composite compared to uncoated PLA material. The finite element analyses that simulated tensile and flexural tests showed consistent computational results with experimental findings.
Strengthening of polylactic acid parts with carbon fiber reinforced polymer composite plates featuring single and double fabric layers in various orientations
(John Wiley and Sons Inc, 2025) Saraç, İsmail; Horasan, Murat; Benli, Semih
This study investigated how coating the surfaces of three-dimensional printed polylactic acid (PLA) parts with carbon fiber fabric-reinforced polymer (CFRP) plates affects their mechanical behavior. The assessment was performed through tensile tests, three-point bending tests, and finite element method analysis. The goal of this study was to enhance the mechanical properties of PLA parts produced through fused deposition modeling (FDM) to expand their applicability in structures. CFRP composites were bonded to the 3D-printed PLA parts using epoxy to create sandwich-structured composite samples. The impact of composite coatings on the mechanical properties of 3D-printed PLA parts was examined in relation to fiber orientation angles and the number of coating layers. Mechanical tests indicated that the tensile and flexural strength of PLA parts coated with CFRP composite was higher than that of uncoated PLA material. In tensile tests, the maximum failure load of uncoated PLA specimens was 861.1 N, whereas the maximum failure load of a composite hybrid structural specimen—fabricated by bonding the PLA with a CFRP composite plate at a 0° orientation angle and employing a double layer of carbon fiber fabric—was 4265 N. Consequently, the increase in failure load was 395%. Finite element analyses simulating the tensile and flexural tests produced results that aligned with the experimental findings. Highlights: CFRP composite plates were fabricated with different ply numbers and fiber orientations. The hybrid structures were produced by bonding CFRP plates with 3D-printed PLA parts. Tensile and flexure tests were performed on hybrid composite structures. Reinforcing 3D-printed PLA with CFRP plates improves mechanical properties.
Investigation on the Effect of Opening Size and Position on Wind-Driven Cross-Ventilation in an Isolated Gable Roof Building
(Multidisciplinary Digital Publishing Institute (MDPI), 2025) Demir, Hacımurat; Aktepe, Burak
In this study, the influence of window opening sizes and positions on wind-induced cross ventilation performance in an isolated gable roof building was numerically investigated using the k-ω SST turbulence model. The results obtained from numerical analyses to evaluate the ventilation efficiency of different configurations show that larger inlet openings significantly increase the ventilation rates and the WO5 model reaches the highest ventilation rate of 0.004089 m3/s with an improvement of 37.27% compared to the reference model. As with the WO1 model, smaller inlet openings limited the air intake, reducing ventilation efficiency and indoor air quality. In terms of outlet window opening sizes, the LO5 model showed the highest ventilation efficiency, improving ventilation by 28% compared to reference model, while smaller outlet openings, as in the LO1 model, were associated with significantly lower performance. Additionally, when evaluating window opening locations, configurations with higher exit openings generally exhibited superior ventilation rates. The best overall ventilation performance was achieved in the Upper-Lower configuration at 0.003129 m3/s. The findings emphasized the critical role of window design in natural ventilation performance. Larger and strategically located window openings optimize airflow, increase ventilation efficiency and improve indoor air quality, providing valuable information for energy-efficient building design.
A numerical comparison of the thermal performances of nano-PCM heat sinks with Fe3O4, MgO, ZnO and xGNP nanoparticles: Key role of increased thermal conductivity
(Elsevier Ltd, 2025) Çiçek, Burcu
A Nano-PCM heat sink model for electronic device cooling was numerically analyzed. RT-35HC was selected as the PCM. Nano-PCMs were created by using different types of nanoparticles, such as Fe3O4, MgO, ZnO and xGNP, added into the PCM at volume fractions of 0.02, 0.04 and 0.06. Nano-PCM heat sinks were numerically simulated in ANSYS under heat fluxes of 3, 4 and 5 kW/m2. Enthalpy-porosity technique was used and UDFs were set in ANSYS for altering the Nano-PCM's thermal conductivity and dynamic viscosity. Results indicate that, by nanoparticles addition, PCM's melting time and heat sink temperature decreased. The reduction in melting time of Nano-PCM were 6.19 %, 10.8 %, and 14.56 % for volume fractions of 0.02, 0.04, and 0.06 for Fe3O4, respectively, relative to PCM only. Initially, the best thermal conductivity was obtained with utilization of xGNP (15 nm), however, with rising temperature over time, thermal conductivity of Nano-PCM with Fe3O4, (10 nm) became the highest. The findings suggest that the lowest base temperature was attained by using Fe3O4, which has the optimum thermal and physical properties, in a 0.02 volume fraction. A detailed and comparative evaluation was provided by addressing various nanoparticles or different sizes of the same nanoparticle for Nano-PCM heat sink.
Characterization of strains induced by in vivo locomotion and axial tibiotarsal loading in a chukar partridge model
(Elsevier Inc., 2025) Horasan, Murat; Verner, Kari A.; Main, Russell P.; Nauman, Eric A.
Rodent models have offered valuable insights into the mechanobiological mechanisms that regulate bone adaptation responses to dynamic mechanical stimuli. However, using avian models may provide new insights into the mechanisms of bone adaptation to dynamic loads, as bird bones have distinct features that differ from mammalian bones. This paper illuminates these aspects by evaluating the mechanical environment in a novel avian, chukar partridge tibiotarsus (TBT), during fast locomotion and in cortical and cancellous tissue under in vivo dynamic compressive loading within the TBT. We measured in vivo mechanical strains at the TBT midshaft on the anterior, medial, and posterior surfaces during locomotion at various treadmill speeds. The mean in vivo strains measured on the anterior, medial, and posterior surfaces of the TBT midshaft were 154 με, -397 με, and -438 με, respectively, at a treadmill speed of 2 m/s. The mean experimentally measured strains on the anterior, medial, and posterior surfaces of the TBT were 114.7 με, -952.6 με, and -593.7 με under an in vivo dynamic compressive load of 130 N. The study, which employs a micro-computed tomography (microCT) based finite element model in combination with diaphyseal strain gauge measures, found that cancellous strains were greater than those in the midshaft cortical bone. Sensitivity analyses revealed that the material property of cortical bone was the most significant model parameter. In the midshaft cortical volume of interest (VOI), daily dynamic loading increased the maximum moment of inertia and reduced the bone area in the loaded limb compared to the contralateral control limb after three weeks of loading. Despite the strong correlations between the computationally modeled strains and experimentally measured strains at the medial and posterior gauge sites, no correlations existed between the computationally modeled strains and strain gradients, and histologically measured bone formation thickness at the mid-diaphyseal cross-section of the TBT.
Investigation on the mechanical properties of Nano-Al2O3 particle reinforced single lap adhesive joints using digimat mean field homogenization and finite element method
(Elsevier Ltd, 2025) Saraç, İsmail; Yıldırım, Ferdi
When the studies on particle reinforced adhesive joints are evaluated, there is a deficiency in simulation methods. Considering the diversity of particles and the variability of reinforcement ratios, obtaining the mechanical properties of particle reinforced adhesives experimentally is a costly process with a high workload. In this study, the mechanical properties of single-lap adhesive joints (SLJs) produced with pure DP460 and 4 % nano-Al2O3 reinforced DP460 epoxy composite adhesive were investigated using Digimat Mean Field Homogenization and Finite Element Method (FEM). At first, bulk and SLJs specimens were produced from composite and pure adhesives to perform experimental studies. Next, based on the experimental studies, finite element analysis (FEA) of the bulk specimens and SLJs was conducted. In the FEM, the Digimat-Mean Field (Digimat-MF) homogenization approach and Ansys structural analysis were employed together. In the first step of the simulation studies, the mechanical properties of the nano-composite adhesive were obtained using the Digimat-MF homeogenization method. In the second step, Digimat interface was created in the Ansys program and material properties were defined. In this way, the structural analysis of nano-Al2O3 reinforced bulk specimens and SLJs were accurately analyzed. In the FEA, tensile strength values of bulk specimens of pure DP460 and 4 % nano-Al2O3 reinforced DP460 epoxy adhesives were obtained. At the end of the study, experimental and simulation data were verified and compared. When the data acquired were evaluated, it was seen that the Digimat-MF homogenization approach and Ansys FEM were successfully applied to adhesive joints containing composite adhesives.
Electrochemical and Thermal Analysis of Lithium-Ion Battery Pack With Different Cell Configurations
(John Wiley and Sons Inc, 2024) Namaldı Kömürcü, Büşra; Elden, Gülşah; Çelik, Muhammet; Genç, Mustafa Serdar
The primary purpose of this research is to analyze and evaluate the effects of various discharge rates and cell configurations on the electrochemical and thermal behavior of a Li-ion battery pack that is exposed to ambient air throughout the discharge process. The three-dimensional numerical model is designed to accomplish this purpose and discusses two different cases. While the discharge rate is changed from 0.5 C to 2 C (stepping by 0.5 C) for each cell configuration considered in the first case, the numerical solutions are obtained for the various cell configurations (6S4P and 8S3P) by keeping the discharge rate constant at 1 C. The results obtained from these solutions show that the discharge rate affects a considerable amount of the battery performances and discharge times of the battery packs, activation, and ohmic losses occurring inside each battery cell. Moreover, 6S4P discharges over a longer period (about 25%) than 8S3P. While both activation and ohmic losses decrease with the increase of discharge rate, these losses remain almost constant at 0.5 C discharge rate in all analyzed conditions. As a result, having a battery pack with a long discharge time while maintaining low temperatures is useful and desired. With this in mind, while evaluating battery packs, the 6S4P battery pack looks to have the best arrangement.
The torsional characterization of 3D-Printed polylactic acid parts with alternating additive manufacturing parameters
(John Wiley and Sons Ltd, 2024) Saraç, İsmail; Horasan, Murat
Three-dimensional (3D) printed polymer parts can be subjected to torsional loads in accordance with the conditions of use. Understanding the torsional properties of 3D printed polymers depending on the printing parameters is a significant research topic in fused deposition modeling (FDM) additive manufacturing processes to be used as machine parts operating under torsional load, such as polymer parts manufactured by extrusion method. Some studies have shown that raster angle and printing speed affect the mechanical properties of 3D-printed polymers. However, tensile tests were used in most of those studies. In this study, the torsional behavior of 3D printed Polylactic acid (PLA) materials was investigated by static torsion tests, finite element analyses, and theoretical and failure analyses with respect to the printing speed and raster angle parameters. Torsion test specimens were manufactured at five different raster angles (0°, 30°, 45°, 60°, and 90°) and two different printing speeds (20 and 80 mm/s) from PLA material using the FDM additive manufacturing method. The results showed that raster angle and printing speed parameters affected the torsional load-carrying capacity of FDM-3D printed PLA parts. The best load-carrying capacity was achieved at 30° and 60° raster angles, while the lowest was measured at 0° raster angle. The torsional load-carrying capacity was significantly enhanced by 85% for specimens manufactured at the printing speed of 80 mm/s.
Thermal stress analysis of maxillary dentures with different reinforcement materials under occlusal load using finite element method
(Multidisciplinary Digital Publishing Institute (MDPI), 2024) Benli, Semih; Baş, Gökhan
The purpose of this study was to determine the effect of fiber reinforcement materials on the magnitude of stresses in a critical part of the maxillary denture base under thermal and occlusal load. Thermal stress analyses of the models were carried out using the finite element method. The models consisted of bone, soft tissue, interface gap, and maxillary dentures with and without reinforcements. A concentrated occlusal load of 230 N was applied bilaterally on the molar teeth. A 36 °C reference and 0 °C, 36 °C, and 70 °C variable ambient temperatures were applied to the models. CrCo, unidirectional and woven carbon/epoxy, unidirectional and woven glass/epoxy, and unidirectional and woven Kevlar/epoxy were used as reinforcing materials in the maxillary denture base made of PMMA (polymethyl methacrylate). Stress distributions on the maxillary denture’s midline and lateral line direction were evaluated. Maximum stresses in the incisal notch and the labial frenal notch of the maxillary denture were determined. Failure analysis of reinforcement materials used in maxillary dentures was carried out using the Tsai-Wu index criterion. The results obtained show that the thermal properties of reinforcement materials should be considered as an important criterion in their selection.
Impact of Window Opening Shapes on Wind-Driven Cross Ventilation Performance in a Generic Isolated Building: A Simulation Study
(Gazi Üniversitesi, 2024) Aktepe, Burak; Demir, Hacımurat
Both environmental concerns and sustainable development goals have led to the search for alternative energy-efficient solutions. Natural ventilation, a crucial aspect of energy-efficient building design, reduces dependence on mechanical systems and regulates indoor air quality and temperature using natural forces. It improves indoor air quality, reduces energy consumption, and lowers operating costs. This paper presents a computational fluid dynamics analysis of natural cross-ventilation in an isolated building with varying window opening geometries. u/uref showed a marked decrease in triangular geometries, while trapezoidal and reference geometries exhibited comparable declines. The airflow velocity profile revealed a U-shaped curve, with reductions observed within 0
Improvement of the Thermal Performance of PCM-Based Heat Sink Used in Electronic Cooling by Adding Nanoparticles
(Gazi Üniversitesi, 2024) Çiçek, Burcu
Recently, thanks to the technological advances, electronic devices are getting smaller in size. This causes an increase in the heat generation per unit area. This heat has to be removed from electronic devices for them to be longer-lasting, more efficient and more reliable. There are many active and passive methods designed for this objective. One of them is embedding phase change material (PCM) in the heat sink. PCM, during the phase change stage, absorbs the heat generated in the system and thus aids in keeping the temperature at a certain value. The biggest downside of PCM is its rapid conduction of heat. PCM properties can be improved by using nanoparticles. In this study, nanoparticles such as TiO2 and CuO were added to PCM and such a modified PCM is used in a finned heat sink. The thermal behavior of the PCM with addition of 1%, 2% and 5% TiO2 and CuO was investigated numerically in three dimensions. RT-28HC was used as the PCM in the study. It was shown that as the nanoparticle ratio increases, heat transfer coefficient of the PCM rises and the melting time of Nanoparticle PCM (NPPCM) is less than that of pure PCM. However, it was observed that, the melting time of PCM with CuO added is longer than that of the PCM with TiO2 added.
Computationally derived endosteal strain and strain gradients correlate with increased bone formation in an axially loaded murine tibia model
(Elsevier Ltd, 2024) Horasan, Murat; Verner, Kari A.; Yang, Haisheng; Main, Russell P.; Nauman, Eric A.
Osteoporosis is a common metabolic bone disorder characterized by low bone mass and microstructural degradation of bone tissue due to a derailed bone remodeling process. A deeper understanding of the mechanobiological phenomena that modulate the bone remodeling response to mechanical loading in a healthy bone is crucial to develop treatments. Rodent models have provided invaluable insight into the mechanobiological mechanisms regulating bone adaptation in response to dynamic mechanic stimuli. This study sheds light on these aspects by means of assessing the mechanical environment of the cortical and cancellous tissue to in vivo dynamic compressive loading within the mouse tibia using microCT-based finite element model in combination with diaphyseal strain gauge measures. Additionally, this work describes the relation between the mid-diaphyseal strains and strain gradients from the finite element analysis and bone formation measures from time-lapse in vivo tibial loading with a fluorochrome-derived histomorphometry analysis. The mouse tibial loading model demonstrated that cancellous strains were lower than those in the midshaft cortical bone. Sensitivity analyses demonstrated that the material property of cortical bone was the most significant model parameter. The computationally-modeled strains and strain gradients correlated significantly to the histologically-measured bone formation thickness at the mid-diaphyseal cross-section of the mouse tibia.
Flow and heat transfer analysis of submerged multiple synthetic jet impingement in a square channel with forced-flow
(Elsevier Ltd, 2024) Akdağ, Ünal; Akçay, Selma; Kılıç, Mustafa; Güngör, Bekir
This study experimentally and numerically investigated the flow and heat transfer of submerged multiple synthetic jet impingement in forced crossflow in a square-section channel with a constant heat flux on the bottom surface. In the forced channel flow, effects on heat transfer of six synthetic jets placed diagonally in the main flow have four different amplitudes and six different frequencies at various Reynolds numbers (6000 ? Re ? 40000) were examined. Jets were submerged vertically into the main flow and their effects on heat transfer in the turbulent regime of the main flow were analyzed. Temperature measurements were made using thermocouples placed at the channel entrances and exits on the target surface. The Nusselt numbers (Nu) were calculated using the measured temperatures. The results indicate that at Re = 6000, the target surface temperature decreases significantly with increasing amplitude and frequency, and the effects of amplitude and frequency on surface temperatures decreased at increasing Reynolds numbers. It was observed that the THP values increased with increasing amplitude and frequency for all Reynolds numbers tested. For a constant jet parameter (Ao = 0.88 and Wo = 27), the highest THP was determined as 2.06 at Re = 6000.
Design and optimization of hybrid renewable energy systems for hydrogen production at Aksaray University campus
(Institution of Chemical Engineers, 2024) Demir, Hacımurat; Demir, Hacımurat
In this study, an off-grid HRES is proposed to ensure the electricity demands of the campus in a reliable, cost-effective, and non-polluting way for Aksaray University to have a sustainable and green campus. Within this framework, three HRESs were designed and compared using HOMER Pro software to find the optimum HRES, using a combination of different components related to zero carbon emissions and fully renewable energy sources, including transportation with environmentally friendly hydrogen fuel cell buses for students, academics, and staff. According to the optimization results obtained for the various configurations, the optimum HRES has a net cost of $20.3 million for the 25-year project life, with annual costs of $1.57 million. The levelized cost of electricity of the proposed system, represented by Scenario III, is calculated to be 0.327$/kWh. The PV panels produce 4,758,497 kWh/year at a levelized cost of 0.0404$/kWh, while the wind turbines produce electricity at a levelized cost of 0.0625$/kWh. The optimal system includes a 2000 kW electrolyzer that produces 73,061 kg of hydrogen annually, with a consumption rate of 46.4 kWh/kgH2. The hydrogen tank has an energy reserve of 83,333 kWh with a storage capacity of 2500 kg. The results indicate that Scenario III is a robust, cost-effective, and environmentally friendly energy solution for the campus, paving the way for a greener future. Furthermore, the proposed HRES model provides a practical framework that can influence campus energy policies and potentially serves as a model for other educational institutions that are interested in implementing sustainable energy solutions.
Yapıştırma bağlantılarında hasar kriterlerinin incelenmesi
(Van Yüzüncü Yıl Üniversitesi, 2024) Saraç, İsmail
Yapıştırıcıların endüstriyel uygulamalarda kullanımının artmasıyla birlikte, yapıştırma bağlantılarında hasar analiz çalışmaları yapılmaya başlanmıştır. Yapılan çalışmalar, yapıştırma bağlantılı yapıların tasarımında mühendisler için önemli bilgiler sunmuş ve tasarımların şekillenmesine katkı sağlamıştır. Yapıştırma bağlantılarının mukavemetini tahmin etmeye yönelik ilk çalışmalar analitik yaklaşımlar kullanılarak yapılmıştır. Bunu takiben, Sonlu Elemanlar Yönteminin yaygınlaşmasıyla birlikte, geometri sınırlaması olmaksızın, yapıştırma bağlantılarının dayanım tahminleri kapsamlı bir şekilde yapılmaya başlanmıştır. Yapıştırıcılar için literatürde çok sayıda hasar kriteri mevcuttur. Hasar kriteri seçiminde, kullanılan yapıştırıcının sünek veya gevrek yapıda olduğunun bilinmesi önemlidir. Ayrıca, yapıştırıcı hasar kriterinin uygulanabilmesi için, yapıştırıcı tabakasının, bağlantının toplam mukavemetinin en zayıf kısmı olması gerekir. Bu çalışmada, gevrek karakterli Araldite AV138 ve sünek yapıda olan Araldite 2015 yapıştırıcılar kullanılarak oluşturulan tek tesirli bindirme bağlantılarında analitik ve sayısal yöntemler kullanılarak hasar yükleri hesaplanmıştır. Elde edilen analitik ve sayısal hasar yükleri literatürdeki bir deneysel çalışma ile karşılaştırılarak, yapıştırıcı plastik davranışının, hasar kriteri seçiminde önemi gösterilmiştir. Çalışma sonucunda, gevrek karakterli yüksek dayanımlı AV138 yapıştırıcının kullanıldığı tek tesirli yapıştırma bağlantılarında Von Mises kriterinin, sünek yapıdaki Araldite 2015 yapıştırıcının kullanıldığı tek tesirli yapıştırma bağlantılarında ise Global Akma kriterinin kullanılmasının incelenen diğer yöntemlere göre daha uygun olduğu gösterilmiştir.
Numerical investigation on thermal behaviors of Heat Sinks and Hybrid Heat Sinks with different PCMs for electronic cooling
(SAGE Publications Inc., 2024) Çiçek, Burcu
In this study, a numerical method was used to investigate the melting process of PCM-Heat Sink and PCM-Hybrid Heat sinks for electronic cooling. Firstly, three different PCMs, designated as RT-28HC, RT-31, and RT-54HC, with varying thermophysical properties, were used within aluminum finned heat sink and three-dimensional time-dependent analyses was conducted using the ANSYS Fluent software, at heat fluxes of 3.6, 4.2, and 4.8 kW/m2. To calculate the enhancement ratio in the PCM-Heat Sink, setpoint temperatures of 45°C and 60°C were selected. The results revealed that RT-54HC is the best option among them, since it produced the lowest heat sink base temperature at the end of 120 min simulation period. At last, two hybrid heat sink models, designated as HPCM1 and HPCM2 were designed and their cooling performances were analyzed at heat transfer coefficients of 5, 10, and 15 W/m K. The RT-54HC was used as the PCM for hybrid heat sinks at a heat flux of 4.8 kW/m2. It was observed that HPCM1, with heat conductivity coefficients of 10 and 15 W/m2 K were more effective than PCM-HS models for cooling. In conclusion, this study provides useful guidelines for designing heat sinks and selecting PCM types for electronic cooling.
The fatigue responses of 3D-printed polylactic acid (PLA) parts with varying raster angles and printing speeds
(John Wiley and Sons Inc, 2024) Horasan, Murat; Saraç, İsmail
In this study, the fatigue behavior of FDM-3D printed polylactic acid (PLA) materials was investigated by rotary bending fatigue tests and finite element studies with varying printing speed and raster angle parameters. Fatigue test specimens were manufactured at five different raster angles (0°, 30°, 45°, 60°, and 90°) and two different printing speeds (20 and 80 mm/s). The effect of printing speed was evaluated at high print speed variation range (20 and 80 mm/s print speeds). It was noticed that the change in raster angle affects the fatigue life very significantly. The highest fatigue life was obtained at 30° raster angle, while the lowest fatigue life was found at 90° raster angle. Increasing the printing speed from 20 to 80 mm/s decreased the fatigue life of all specimens. The derived results from the finite element analyses were consistent with the experimental results.
Energy recovery and hydrogen production potential assessment in a natural gas pressure reduction station
(Elsevier, 2024) Ermiş, Musa; Çelik, Muhammet
An energy recovery and hydrogen production potential assessment study was carried out for a pressure reduction station by integrating a turbo expander-electrolyzer system. The hydrogen and electricity production potentials were investigated based on the natural gas flow rate. For this purpose, a turbo expander-proton exchange membrane electrolyzer system was considered, using standard data of an RMS-A type PRS. The variation in energy recovery potential was calculated according to the natural gas flow rate and inlet-outlet parameters such as temperature and pressure. By using these parameters, energy balance calculations and energy profit rate were evaluated. The energy profit rate was calculated as 274 kWh for 50.000 Sm3/h volumetric flow rate. Based on real data for a PRS, the electricity and hydrogen production potential were found to be 13.654.567?kW of electricity and 1.532.325,6 Nm3 of hydrogen production with the annual natural gas flow. According to the sensitivity analysis, increasing the station inlet temperature and outlet pressure negatively affected the energy profit rate, while increasing the inlet pressure had a positive effect. The levelized cost of electricity was calculated as 0,056 $/kW, while the levelized cost of hydrogen was found to be 1,989 $/kgH2. These results indicate that energy recovery from the PRSs is feasible and an opportunity to ensure sustainability.
Experimental investigation of the heat transfer characteristics of a synthetic annular jet impingement on a flat surface
(Taylor and Francis Ltd., 2025) Akdağ, Ünal; Akçay, Selma; Ün, Necati; Danışmaz, Merdin
Annular impinging jets create a more uniform flow on the impact surface compared to circular impinging jets, allowing the surface to cool better. Additionally, periodic flow oscillations significantly increase heat transfer by reducing the thermal resistance on the surface. Therefore, this study experimentally investigated the heat transfer characteristics of a synthetic annular jet impinging on a flat surface with constant heat flux. In the experiments, the jet-target surface distance (H/D), jet Reynolds number (Rej), oscillation amplitude (Ao), and Womersley number (Wo) were changed. In contrast, the Prandtl number (Pr) and other geometric parameters were kept constant. The effects of these parameters on heat transfer were analyzed and the results were compared with continuous circular and annular impinging jets. Local temperature values on the target surface were obtained for different parameters and heat transfer from the surface was calculated. Experimental results showed that heat transfer increased with decreasing H/D ratio for all jet types. The highest heat transfer on the surface was achieved in synthetic jet flow. Heat transfer increased as the oscillation amplitude decreased.

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